1. Field of the Invention
The present invention relates to a digital TV, and more particularly, to an apparatus for converting a video format of a digital TV and method thereof.
2. Discussion of the Related Art
Currently, there are various kinds of video signal specifications and display devices representing to enable a user to view the video.
The video signal specifications include analog TV signal (e.g., NTSC, PAL, SECAM, etc.), VCR signal, PC signal (VGA˜UXGA), recent digital TV signal (e.g., ATSC, DVB, ARIB), and the like.
And, the display devices for displaying the video signals include CRT, projection system, PDP (plasma display panel), LCD (liquid crystal display), and the like.
At the beginning era of digital broadcasting, demands for digital TV to support the various video specifications and display devices will rise.
SOC (system-on-chip) is realized due to the development of semiconductor processes, thereby enabling to implement various complicated functions on one chip.
Digital TV supports a multi-format via one specification unlike the conventional analog TV.
For instance, ATSC standards as U.S. terrestrial digital TV broadcasting standards support eighteen video formats so that a broadcasting station may select one of them.
The eighteen formats supported by ATSC are shown in Table 1.
TABLE 1SpatialAspectresolutionFrame rate/scanratioFormat No.1920 * 108024P, 30P, 30I16:931280 * 720 24P, 30P, 60P16:93704 * 48024P, 30P, 30I, 60P16:94″ 4:34640 * 48024P, 30P, 30I, 60P 4:34
In Table 1, video format means spatial resolution, frame rate, scanning system, and aspect ratio.
In order to enable transmission of various formats, a digital TV receiver needs to support various input formats. Namely, a digital TV receiver should be equipped with a function of converting various input formats into requested output formats to fit the corresponding format of its display device.
FIG. 1 is a diagram of a principle of video format conversion.
Referring to FIG. 1, a predetermined processing is performed on N-input formats to convert into N-output formats.
A digital TV format converting unit adopts a method of converting four formats including resolution, frame rate, scanning system, and aspect ratio.
FIG. 2 is a block diagram of a format converting device of a general digital TV, in which it is assumed that VSB (vestigial sideband) modulation is performed on an RF type TV signal.
Referring to FIG. 2, a VSB demodulator 201 demodulates an inputted RF type digital TV signal to output to a TS demultiplexer 202 via TS (transport stream) form. The TS demultiplexer 202 selects one of a plurality of programs included in one channel, separates audio bit stream and video bit stream, which are multiplexed in the selected program, from each other, and then outputs the separated video bit stream to an MPEG2 (motion picture experts group 2) video decoder 203 and the separated audio bit stream to an audio decoder 205.
The MPEG2 video decoder 203 performs variable length decoding (VLD) on pure data information resulting from removing overheads (various header information, start code, etc.) from the inputted video bit stream, restores an original pixel value via motion compensation using de-quantization, IDCT (inverted discrete cosine transform), and motion vector, and then outputs the restored pixel value to a format converting unit 204.
And, the audio decoder 205 restores an original audio signal from the inputted audio bit stream using MPEG algorithm, audio coding algorithm (AC-3), or the like and then outputs the restored original audio signal to a speaker and the like.
The format converting unit 204 extracts four kinds of format information included in a digital broadcast signal transmitted from a broadcasting station, i.e., resolution, frame rate, scanning system, and aspect ratio, and converts the broadcast signal into a video format fitting a display device using them (ex. 1920×1080 30i(16:9), where ‘i’ indicates interlace scan).
However, the related art video format converting device has the following problems or disadvantages.
First of all, the video format converting device needs a separate format converter to support an analog signal as well as a digital TV signal. Namely, the video format converting device fails to include a format converting unit for processing other video signals such as an analog signal despite having the digital TV signal format converting unit. Hence, an auxiliary format converting unit, as shown in FIG. 3, is further needed.
Referring to FIG. 3, an auxiliary format converting unit 301 performing format conversion on analog TV signal, PC signal, component signal, and the like is added to the construction of FIG. 2. In this case, a video signal format-converted in the digital TV format converting unit 204 or the auxiliary format converting unit 301 is selected via a multiplexer 302 to be outputted.
Secondly, the analog signal fails to include format information therein. In digital TV signal, format information is attached to a header to be transmitted so that the format information can be extracted from the header. Yet, it is unable to detect format information from the analog video signal failing to have such information. Hence, a device for detecting format information is further needed.
Thirdly, in case that the video format converting device needs to support an analog signal, a separate color space and chroma format converter is further needed.
Hence, the auxiliary format converting unit 301 in FIG. 3 is developed into a construction shown in FIG. 4 to settle the above problems.
For instance, an inputted NTSC composite signal is separated into a horizontal/vertical sync signal, a brightness signal Y, and a color signal C. If necessary, the signals pass through color space conversion (e.g., YIQ→YCbCr) and chroma format conversion (e.g., 4:4:4→4:2:2) in a color converting unit 404 to be inputted to a format converting unit 406.
Moreover, a PC signal (VGA˜UXGA) is inputted as an RGB form via an RGB input unit 402. If necessary, the PC signal pass through color space conversion (e.g., RGB→YCbCr) and chroma format conversion (e.g., 4:4:4→4:2:2) in a color converting unit 405 to be inputted to the format converting unit 406. And, a component signal (480i˜1080i) is inputted to the format converting unit 406 via an input unit 403 without passing through color conversion.
Thus, in order to handle external video signals including analog TV signal, PC signal, component signal, and the like, the related art needs the separate device performing color space conversion and chroma format conversion in FIG. 4.
FIG. 5 is a diagram of an example of conversion between various color spaces. For instance, if a color space of an input video is GBR and a color space of a requested output video is YIQ, a corresponding relation is expressed by Equation 1.
                                          (                                                            Y                                                                              I                                                                              Q                                                      )                    =                                    1              256                        ⁢                          (                                                                    150                                                        29                                                        77                                                                                                              -                      70                                                                                                  -                      82                                                                            153                                                                                                              -                      134                                                                            80                                                        54                                                              )                        ⁢                          (                                                                    G                                                                                        B                                                                                        R                                                              )                                      ⁢                                  ⁢                                                            Y                =                                                      1                    256                                    ⁢                                      (                                                                  150                        ×                        G                                            +                                              29                        ×                        B                                            +                                              77                        ×                        R                                                              )                                                                                                                          I                =                                                      1                    256                                    ⁢                                      (                                                                                            -                          70                                                ×                        G                                            -                                              82                        ×                        B                                            +                                              153                        ×                        R                                                              )                                                                                                                          Q                =                                                      1                    256                                    ⁢                                      (                                                                                            -                          134                                                ×                        G                                            +                                              80                        ×                        B                                            +                                              54                        ×                        R                                                              )                                                                                                          [                  Equation          ⁢                                          ⁢          1                ]            
Fourthly, in case that the video format converting device needs to support various display devices, a separate gamma correction and geometric correction device is needed. Gamma correction means to correct various distortions occurring due to color characteristics of a display device. Hence, all kinds of display devices need gamma correction.
And, geometric correction is to correct various geometric distortions occurring due to display device characteristics shown in FIGS. 6A to 6D. Especially, the geometric distortion becomes serious not in PDP, LCD, and the like but in CRT and projection systems.
Fifthly, in case that the video format converting device supports an image quality adjustment function of brightness, contrast, color, hue, color temperature, and the like, image quality adjustment in an analog area is fine. Yet, in a digital display such as PDP and LCD, an image quality is firstly adjusted by D/A conversion of a video signal and A/D conversion is then executed. Hence, the corresponding image quality tends to be degraded. This is explained as follows by referring to the attached drawings.
FIG. 7A is a block diagram of an image quality adjusting unit of an analog display device according to a related art.
Referring to FIG. 7A, a digital signal converted via a format converting unit 701 is converted to an analog signal by a D/A converting unit 702 so that an image quality is adjusted in an image quality adjusting unit 703. Hence, an analog display is free from image quality degradation.
Yet, in a digital display, as shown in FIG. 7B, a digital signal converted via a format converting unit 701 is converted to an analog signal by a D/A converting unit 702 to be adjusted in an image adjusting unit 703. And, the adjusted analog signal is then converted again to a digital signal by an A/D converting unit 704 to be outputted, thereby bringing about the image quality degradation.